boxes = tf.constant([[4.0, 3.0, 7.0, 5.0],
                           [5.0, 6.0, 10.0, 7.0],
                           [3.0, 4.0, 6.0, 8.0],
                           [14.0, 14.0, 15.0, 15.0],
                           [0.0, 0.0, 20.0, 20.0]])